The advent of a new round of stringent emissions legislation in Europe and North
America is driving the implementation of new exhaust after-treatment systems, particularly for lean-burn technologies such as compression-ignition (diesel) engines, and stratified-charge spark-ignited engines (usually with direct injection) that are operating under lean and ultra-lean conditions. Lean-burn engines exhibit high levels of nitrogen oxide (NOx) emissions that are difficult to treat in oxygen-rich exhaust environments characteristic of lean-burn combustion. Exhaust after-treatment technologies are currently being developed that will treat NOx under these conditions. One of these technologies comprises a catalyst that facilitates the reactions of ammonia (NH3) with the exhaust nitrogen oxides (NOx) to produce nitrogen (N2) and water (H2O). This technology is referred to as Selective Catalytic Reduction (SCR).
Ammonia is difficult to handle in its pure form in the automotive environment. Therefore, it is customary with these systems to use a liquid aqueous urea solution, typically at a 32% concentration of urea solution (CO (NH2)2). The solution is referred to as AUS-32, and is also known under its commercial name of AdBlue. The urea solution is delivered to the hot exhaust stream by an injector and the urea solution is transformed into ammonia in the exhaust after undergoing thermolysis, or thermal decomposition, into ammonia and isocyanic acid (HNCO). The isocyanic acid then undergoes a hydrolysis with the water present in the exhaust and is transformed into ammonia and carbon dioxide (CO2). The ammonia resulting from the thermolysis and the hydrolysis then undergoes a catalyzed reaction with the nitrogen oxides as described previously.
A conventional urea injector is shown generally indicated at 10 in FIG. 1. The injector 10 includes an inlet connector 12 defining an inlet 14 of the injector. An inlet cup 16 is coupled to the inlet connector 12. An inlet tube 17 is coupled to a body 24 of the injector 10 and delivers urea solution to a solenoid 18 that is housed in the body 24. The electrically operated solenoid 18 controls the amount of urea solution delivered from an outlet 20 of the injector and into the exhaust gas flow path of a vehicle in a dosing application. The solenoid 18 can be of the type disclosed in U.S. Pat. No. 6,685,112, the content of which is hereby incorporated by reference into this specification. As best shown in FIG. 2, a conventional elastomeric O-ring seal 22 of round cross-section is provided between the inlet cup 16 and inlet tube 17 of the injector 10. Normal urea solution flow through the injection 10 is shown by the vertical arrow A directed downwardly.
In the conventional injector 10, improper sealing can occur between the seal 22 and the body 24, which can result in the intrusion of water or other liquids (shown by arrows B in FIG. 2) into the interior of the injector 10. Any conductive liquid such as salt water is known to cause bridging of electrical paths and subsequent injector failure. This is particularly troublesome on a urea injector which is mounted underbody and is exposed to a harsher environment than a gasoline injector. Continuous wetting from rain or melted snow is likely. Salts used to melt ice in northern climates create a very conductive liquid due to the ionic nature of sodium chloride.
Thus, there is a need in a urea injector to provide improved sealing structure to prevent the intrusion of external liquid into an interior of the injector.